Heart regeneration and the cardiomyocyte cell cycle

Clinical value of BRE-AS1 in myocardial infarction and its role in myocardial infarction-induced cardiac muscle cell apoptosis

Objectives. The aim of this study was to investigate the expression of long non-coding RNA (lncRNA) brain and reproductive organ-expressed protein (BRE) antisense RNA 1 (BRE-AS1) in patients with acute myocardial infarction (AMI) and its effect on ischemia/reperfusion (I/R)-induced oxidative stress and apoptosis of cardiomyocytes. Methods. Serum BRE-AS1 levels in patients with AMI was detected using quantitative real-time polymerase chain reaction (qRT-PCR). The diagnostic and prognostic values of BRE-AS1 were evaluated. H9c2 cells were treated with hypoxia/reoxygenation to establish an in vitro myocardial infarction cell model. The levels of inflammatory cytokines such as tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and IL-6 were detected by enzyme-linked immunosorbent assay (ELISA). Levels of lactate dehydrogenase (LDH), malondialdehyde (MDA), superoxide dismutase (SOD), and glutathione peroxidase (GSH-Px) were determined by commercial kits. Cell counting kit-8 (CCK-8) and flow cytometry were used to evaluate the cell viability and cell apoptosis. Results. The expression of BRE-AS1 in serum of patients with AMI is upregulated, which shows the clinical diagnostic value for AMI. In the I/R injury cell model, the knockout of BRE-AS1 can significantly alleviate the increase in TNF-α, IL-1β, and IL-6 levels, inhibit the production of LDH and MDA, increase the activities of SOD and GSH-Px, promote the cell viability and suppress cell apoptosis. Conclusions. Abnormally elevated BRE-AS1 has a high diagnostic value for AMI as well as a prognostic value for major adverse cardiovascular events (MACEs). The elevation of BRE-AS1 promoted oxidative stress injury and cell apoptosis in vitro.

Advancing Cardiomyocyte Maturation: Current Strategies and Promising Conductive Polymer-Based Approaches

Cardiovascular diseases are a leading cause of mortality and pose a significant burden on healthcare systems worldwide. Despite remarkable progress in medical research, the development of effective cardiovascular drugs has been hindered by high failure rates and escalating costs. One contributing factor is the limited availability of mature cardiomyocytes (CMs) for accurate disease modeling and drug screening. Human induced pluripotent stem cell-derived CMs offer a promising source of CMs; however, their immature phenotype presents challenges in translational applications. This review focuses on the road to achieving mature CMs by summarizing the major differences between immature and mature CMs, discussing the importance of adult-like CMs for drug discovery, highlighting the limitations of current strategies, and exploring potential solutions using electro-mechano active polymer-based scaffolds based on conductive polymers. However, critical considerations such as the trade-off between 3D systems and nutrient exchange, biocompatibility, degradation, cell adhesion, longevity, and integration into wider systems must be carefully evaluated. Continued advancements in these areas will contribute to a better understanding of cardiac diseases, improved drug discovery, and the development of personalized treatment strategies for patients with cardiovascular disorders.

Identification and validation of aging-related genes in heart failure based on multiple machine learning algorithms

Background

In the face of continued growth in the elderly population, the need to understand and combat age-related cardiac decline becomes even more urgent, requiring us to uncover new pathological and cardioprotective pathways.

Methods

We obtained the aging-related genes of heart failure through WGCNA and CellAge database. We elucidated the biological functions and signaling pathways involved in heart failure and aging through GO and KEGG enrichment analysis. We used three machine learning algorithms: LASSO, RF and SVM-RFE to further screen the aging-related genes of heart failure, and fitted and verified them through a variety of machine learning algorithms. We searched for drugs to treat age-related heart failure through the DSigDB database. Finally, We use CIBERSORT to complete immune infiltration analysis of aging samples.

Results

We obtained 57 up-regulated and 195 down-regulated aging-related genes in heart failure through WGCNA and CellAge databases. GO and KEGG enrichment analysis showed that aging-related genes are mainly involved in mechanisms such as Cellular senescence and Cell cycle. We further screened aging-related genes through machine learning and obtained 14 key genes. We verified the results on the test set and 2 external validation sets using 15 machine learning algorithm models and 207 combinations, and the highest accuracy was 0.911. Through screening of the DSigDB database, we believe that rimonabant and lovastatin have the potential to delay aging and protect the heart. The results of immune infiltration analysis showed that there were significant differences between Macrophages M2 and T cells CD8 in aging myocardium.

Conclusion

We identified aging signature genes and potential therapeutic drugs for heart failure through bioinformatics and multiple machine learning algorithms, providing new ideas for studying the mechanism and treatment of age-related cardiac decline.

Maternal androgen excess inhibits fetal cardiomyocytes proliferation through RB-mediated cell cycle arrest and induces cardiac hypertrophy in adulthood

PURPOSE

Maternal hyperandrogenism during pregnancy is associated with adverse gestational outcomes and chronic non-communicable diseases in offspring. However, few studies are reported to demonstrate the association between maternal androgen excess and cardiac health in offspring. This study aimed to explore the relation between androgen exposure in utero and cardiac health of offspring in fetal and adult period. Its underlying mechanism is also illustrated in this research.

METHODS

Pregnant mice were injected with dihydrotestosterone (DHT) from gestational day (GD) 16.5 to GD18.5. On GD18.5, fetal heart tissue was collected for metabolite and morphological analysis. The hearts from adult offspring were also collected for morphological and qPCR analysis. H9c2 cells were treated with 75 μM androsterone. Immunofluorescence, flow cytometry, qPCR, and western blot were performed to observe cell proliferation and explore the underlying mechanism.

RESULTS

Intrauterine exposure to excessive androgen led to thinner ventricular wall, decreased number of cardiomyocytes in fetal offspring and caused cardiac hypertrophy, compromised cardiac function in adult offspring. The analysis of steroid hormone metabolites in fetal heart tissue by ultra performance liquid chromatography and tandem mass spectrometry showed that the content of androgen metabolite androsterone was significantly increased. Mechanistically, H9c2 cells treated with androsterone led to a significant decrease in phosphorylated retinoblastoma protein (pRB) and cell cycle-related protein including cyclin-dependent kinase 2 (CDK2), cyclin-dependent kinase 4 (CDK4), and cyclin D1 (CCND1) in cardiomyocytes. This resulted in cell cycle arrest at G1-S phase, which in turn inhibited cardiomyocyte proliferation.

CONCLUSION

Taken together, our results indicate that in utero exposure to DHT, its metabolite androsterone could directly decrease cardiomyocytes proliferation through cell cycle arrest, which has a life-long-lasting effect on cardiac health. Our study highlights the importance of monitoring sex hormones in women during pregnancy and the follow-up of cardiac function in offspring with high risk of intrauterine androgen exposure.

Right ventricular cardiomyocyte expansion accompanies cardiac regeneration in newborn mice after large left ventricular infarcts

Cauterization of the root of the left coronary artery (LCA) in the neonatal heart on postnatal day 1 (P1) resulted in large, reproducible lesions of the left ventricle (LV), and an attendant marked adaptive response in the right ventricle (RV). The response of both chambers to LV myocardial infarction involved enhanced cardiomyocyte (CM) division and binucleation, as well as LV revascularization, leading to restored heart function within 7 days post surgery (7 dps). By contrast, infarction of P3 mice resulted in cardiac scarring without a significant regenerative and adaptive response of the LV and the RV, leading to subsequent heart failure and death within 7 dps. The prominent RV myocyte expansion in P1 mice involved an acute increase in pulmonary arterial pressure and a unique gene regulatory response, leading to an increase in RV mass and preserved heart function. Thus, distinct adaptive mechanisms in the RV, such as CM proliferation and RV expansion, enable marked cardiac regeneration of the infarcted LV at P1 and full functional recovery.

Quercetin and dasatinib, two powerful senolytics in age-related cardiovascular disease

Cellular senescence is characteristic of the development and progression of multiple age-associated diseases. Accumulation of senescent cells in the heart contributes to various age-related pathologies. Several compounds called senolytics have been designed to eliminate these cells within the tissues. In recent years, the use and study of senolytics increased, representing a promising field for finding accessible and safe therapies for cardiovascular disease (CVD) treatment. This mini-review discusses the changes in the aging heart and the participation of senescent cells in CVD, as well as the use of senolytics to prevent the progression of myocardial damage, mainly the effect of dasatinib and quercetin. In particular, the mechanisms and physiological effects of senolytics therapies in the aged heart are discussed.

Morroniside induces cardiomyocyte cell cycle activity and promotes cardiac repair after myocardial infarction in adult rats

Introduction: Acute myocardial infarction (AMI) is characterized by the loss of cardiomyocytes, which impairs cardiac function and eventually leads to heart failure. The induction of cardiomyocyte cell cycle activity provides a new treatment strategy for the repair of heart damage. Our previous study demonstrated that morroniside exerts cardioprotective effects. This study investigated the effects and underlying mechanisms of action of morroniside on cardiomyocyte cell cycle activity and cardiac repair following AMI. Methods: Neonatal rat cardiomyocytes (NRCMs) were isolated and exposed to oxygen-glucose deprivation (OGD) in vitro. A rat model of AMI was established by ligation of the left anterior descending coronary artery (LAD) in vivo. Immunofluorescence staining was performed to detect newly generated cardiomyocytes. Western blotting was performed to assess the expression of cell cycle-related proteins. Electrocardiography (ECG) was used to examine pathological Q waves. Masson's trichrome and wheat germ agglutinin (WGA) staining assessed myocardial fibrosis and hypertrophy. Results: The results showed that morroniside induced cardiomyocyte cell cycle activity and increased the levels of cell cycle proteins, including cyclin D1, CDK4, cyclin A2, and cyclin B1, both in vitro and in vivo. Moreover, morroniside reduced myocardial fibrosis and remodeling. Discussion: In conclusion, our study demonstrated that morroniside stimulates cardiomyocyte cell cycle activity and cardiac repair in adult rats, and that these effects may be related to the upregulation of cell cycle proteins.

Potential Application of Modified mRNA in Cardiac Regeneration

Heart failure remains the leading cause of human death worldwide. After a heart attack, the formation of scar tissue due to the massive death of cardiomyocytes leads to heart failure and sudden death in most cases. In addition, the regenerative ability of the adult heart is limited after injury, partly due to cell-cycle arrest in cardiomyocytes. In the current post-COVID-19 era, urgently authorized modified mRNA (modRNA) vaccines have been widely used to prevent severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Therefore, modRNA-based protein replacement may act as an alternative strategy for improving heart disease. It is a safe, effective, transient, low-immunogenic, and integration-free strategy for in vivo protein expression, in addition to recombinant protein and stem-cell regenerative therapies. In this review, we provide a summary of various cardiac factors that have been utilized with the modRNA method to enhance cardiovascular regeneration, cardiomyocyte proliferation, fibrosis inhibition, and apoptosis inhibition. We further discuss other cardiac factors, modRNA delivery methods, and injection methods using the modRNA approach to explore their application potential in heart disease. Factors for promoting cardiomyocyte proliferation such as a cocktail of three genes comprising FoxM1, Id1, and Jnk3-shRNA (FIJs), gp130, and melatonin have potential to be applied in the modRNA approach. We also discuss the current challenges with respect to modRNA-based cardiac regenerative medicine that need to be overcome to apply this approach to heart disease. This review provides a short description for investigators interested in the development of alternative cardiac regenerative medicines using the modRNA platform.

Glucocorticoid Receptor Antagonism and Cardiomyocyte Regeneration Following Myocardial Infarction: A Systematic Review

Myocardial regeneration has been a topic of interest in literature and research in recent years. An evolving approach reported is glucocorticoid (GC) receptor antagonism and its role in the regeneration of cardiomyocytes. The authors of this study aim to explore the reported literature on GC receptor antagonism and its effects on cardiomyocyte remodeling, hypertrophy, scar formation, and ongoing cardiomyocyte death following cardiac injury. This article overviews cellular biology, mechanisms of action, clinical implications, challenges, and future considerations. The authors of this study conducted a systematic review utilizing the Cochrane methodology and PRISMA guidelines. This study includes data collected and interpreted from 30 peer-reviewed articles from 3 databases with the topic of interest. The mammalian heart has regenerative potential during its embryonic and fetal phases which is lost during its developmental processes. The microenvironment, intrinsic molecular mechanisms, and systemic and external factors impact cardiac regeneration. GCs influence these aspects in some cases. Consequently, GC receptor antagonism is emerging as a promising potential target for stimulating endogenous cardiomyocyte proliferation, aiding in cardiomyocyte regeneration following a cardiac injury such as a myocardial infarction (MI). Experimental studies on neonatal mice and zebrafish have shown promising results with GC receptor ablation (or brief pharmacological antagonism) promoting the survival of myocardial cells, re-entry into the cell cycle, and cellular division, resulting in cardiac muscle regeneration and diminished scar formation. Transient GC receptor antagonism has the potential to stimulate cardiomyocyte regeneration and help prevent the dreaded complications of MI. More trials based on human populations are encouraged to justify their applications and weigh the risk-benefit ratio.

Unravelling the Interplay between Cardiac Metabolism and Heart Regeneration

Ischemic heart disease (IHD) is the leading cause of heart failure (HF) and is a significant cause of morbidity and mortality globally. An ischemic event induces cardiomyocyte death, and the ability for the adult heart to repair itself is challenged by the limited proliferative capacity of resident cardiomyocytes. Intriguingly, changes in metabolic substrate utilisation at birth coincide with the terminal differentiation and reduced proliferation of cardiomyocytes, which argues for a role of cardiac metabolism in heart regeneration. As such, strategies aimed at modulating this metabolism-proliferation axis could, in theory, promote heart regeneration in the setting of IHD. However, the lack of mechanistic understanding of these cellular processes has made it challenging to develop therapeutic modalities that can effectively promote regeneration. Here, we review the role of metabolic substrates and mitochondria in heart regeneration, and discuss potential targets aimed at promoting cardiomyocyte cell cycle re-entry. While advances in cardiovascular therapies have reduced IHD-related deaths, this has resulted in a substantial increase in HF cases. A comprehensive understanding of the interplay between cardiac metabolism and heart regeneration could facilitate the discovery of novel therapeutic targets to repair the damaged heart and reduce risk of HF in patients with IHD.

Impact of Non-Muscle Cells on Excitation-Contraction Coupling in the Heart and the Importance of In Vitro Models

Excitation-coupling (ECC) is paramount for coordinated contraction to maintain sufficient cardiac output. The study of ECC regulation has primarily been limited to cardiomyocytes (CMs), which conduct voltage waves via calcium fluxes from one cell to another, eliciting contraction of the atria followed by the ventricles. CMs rapidly transmit ionic flux via gap junction proteins, predominantly connexin 43. While the expression of connexin isoforms has been identified in each of the individual cell populations comprising the heart, the formation of gap junctions with nonmuscle cells (i.e., macrophages and Schwann cells) has gained new attention. Evaluating nonmuscle contributions to ECC in vivo or in situ remains difficult and necessitates the development of simple, yet biomimetic in vitro models to better understand and prevent physiological dysfunction. Standard 2D cell culture often consists of homogenous cell populations and lacks the dynamic mechanical environment of native tissue, confounding the phenotypic and proteomic makeup of these highly mechanosensitive cell populations in prolonged culture conditions. This review will highlight the recent developments and the importance of new microphysiological systems to better understand the complex regulation of ECC in cardiac tissue.

Endothelial Brg1 fine-tunes Notch signaling during zebrafish heart regeneration

Myocardial Brg1 is essential for heart regeneration in zebrafish, but it remains unknown whether and how endothelial Brg1 plays a role in heart regeneration. Here, we found that both brg1 mRNA and protein were induced in cardiac endothelial cells after ventricular resection and endothelium-specific overexpression of dominant-negative Xenopus Brg1 (dn-xbrg1) inhibited myocardial proliferation and heart regeneration and increased cardiac fibrosis. RNA-seq and ChIP-seq analysis revealed that endothelium-specific overexpression of dn-xbrg1 changed the levels of H3K4me3 modifications in the promoter regions of the zebrafish genome and induced abnormal activation of Notch family genes upon injury. Mechanistically, Brg1 interacted with lysine demethylase 7aa (Kdm7aa) to fine-tune the level of H3K4me3 within the promoter regions of Notch family genes and thus regulated notch gene transcription. Together, this work demonstrates that the Brg1-Kdm7aa-Notch axis in cardiac endothelial cells, including the endocardium, regulates myocardial proliferation and regeneration via modulating the H3K4me3 of the notch promoters in zebrafish.

Cardiomyocyte-fibroblast crosstalk in the postnatal heart

During the postnatal period in mammals, the heart undergoes significant remodeling in response to increased circulatory demands. In the days after birth, cardiac cells, including cardiomyocytes and fibroblasts, progressively lose embryonic characteristics concomitant with the loss of the heart’s ability to regenerate. Moreover, postnatal cardiomyocytes undergo binucleation and cell cycle arrest with induction of hypertrophic growth, while cardiac fibroblasts proliferate and produce extracellular matrix (ECM) that transitions from components that support cellular maturation to production of the mature fibrous skeleton of the heart. Recent studies have implicated interactions of cardiac fibroblasts and cardiomyocytes within the maturing ECM environment to promote heart maturation in the postnatal period. Here, we review the relationships of different cardiac cell types and the ECM as the heart undergoes both structural and functional changes during development. Recent advances in the field, particularly in several recently published transcriptomic datasets, have highlighted specific signaling mechanisms that underlie cellular maturation and demonstrated the biomechanical interdependence of cardiac fibroblast and cardiomyocyte maturation. There is increasing evidence that postnatal heart development in mammals is dependent on particular ECM components and that resulting changes in biomechanics influence cell maturation. These advances, in definition of cardiac fibroblast heterogeneity and function in relation to cardiomyocyte maturation and the extracellular environment provide, support for complex cell crosstalk in the postnatal heart with implications for heart regeneration and disease mechanisms.

Gene Therapy for Cardiomyocyte Renewal: Cell Cycle, a Potential Therapeutic Target

Heart disease is the primary cause of death worldwide. Even though extensive research has been done, and many pharmacological and surgical treatments have been introduced to treat heart disease, the mortality rate still remains high. Gene therapy is widely used to understand molecular mechanisms of myocardial infarction and to treat cardiomyocyte loss. It was reported that adult cardiomyocytes proliferate at a very low rate; thus, targeting their proliferation has become a new regenerative therapeutic approach. Currently, re-activating cardiomyocyte proliferation appears to be one of the most promising methods to promote adult cardiomyocyte renewal. In this article, we highlight gene therapeutic targets of cell proliferation presently being pursued to re-activate the cell cycle of cardiomyocytes, including cell cycle regulators, transcription factors, microRNAs, signal transduction, and other contributing factors. We also summarize gene delivery vectors that have been used in cardiac research and major challenges to be overcome in the translation to the clinical approach and future directions.

MicroRNA Expression in the Infarcted Heart Following Neonatal Cardiovascular Progenitor Cell Transplantation in a Sheep Model of Stem Cell-Based Repair

Myocardial infarctions affect approximately 735,000 people annually in the United States and have a substantial impact on quality of life. Neonates have an enhanced capability of repairing cardiovascular damage, while adults do not. The mechanistic basis for this age-dependent difference in regenerative capacity remains unknown. Recent studies have shown that microRNAs (miRNAs) play a significant role in regulating the regenerative ability of cardiovascular cells. This report defines the alterations in miRNA expression within the cardiovascular repair zone of infarcted sheep hearts following intracardiac injection of neonatal islet-1+ cardiovascular progenitor cells. Sheep were infarcted via left anterior descending coronary artery ligation. After 3 to 4 weeks of infarction, sheep neonatal islet-1+ cardiovascular progenitor cells were injected into the infarcted area for repair. Cell-treated sheep were euthanized 2 months following cell injection, and their hearts were harvested for the analysis of miRNA and gene expression within the cardiovascular repair zone. Ten miRNAs were differentially regulated in vivo, including miR-99, miR-100, miR-302a, miR-208a, miR-665, miR-1, miR-499a, miR-34a, miR-133a, and miR-199a. These miRNAs promote stemness, cell division, and survival. Several signaling pathways are regulated by these miRNAs, including Hippo, Wnt, and Erythroblastic Leukemia Viral Oncogene B (ERBB). Transcripts encoding Wnt, ERBB, and Neuregulin 1 (NRG1) were elevated in vivo in the infarct repair zone. Wnt5a signaling and ERBB/NRG1 transcripts contribute to activation of Yes-Associated Protein 1. MiRNAs that impact proliferation, cell survival, and signaling pathways that promote regeneration were induced during cardiovascular repair in the sheep model. This information can be used to design new approaches for the optimization of miRNA-based treatments for the heart.

Precise dapagliflozin delivery by cardiac homing peptide functionalized mesoporous silica nanocarries for heart failure repair after myocardial infarction

Myocardial infarction (MI) may cause irreversible damage or destroy to part of the heart muscle, affecting the heart’s ability and power to pump blood as efficiently as before, often resulting in heart failure (HF). Cardiomyocyte death and scar formation after MI may then trigger chronic neurohormonal activation and ventricular remodeling. We developed a biocompatible and mono-dispersed mesoporous silica nanoparticles (MSN) divergent porous channel for dapagliflozin (DAPA) loading. After surface modification of the cardiac-targeting peptides, the novel drug delivery system was successfully homed, and precisely released drugs for the hypoxic and weak acid damaged cardiomyocytes. Our biocompatible MSN- based nanocarriers for dapagliflozin delivery system could effective cardiac repair and regeneration in vivo, opening new opportunities for healing patients with ischemic heart disease in clinical.

Keeping the beat against time: Mitochondrial fitness in the aging heart

The process of aging strongly correlates with maladaptive architectural, mechanical, and biochemical alterations that contribute to the decline in cardiac function. Consequently, aging is a major risk factor for the development of heart disease, the leading cause of death in the developed world. In this review, we will summarize the classic and recently uncovered pathological changes within the aged heart with an emphasis on the mitochondria. Specifically, we describe the metabolic changes that occur in the aging heart as well as the loss of mitochondrial fitness and function and how these factors contribute to the decline in cardiomyocyte number. In addition, we highlight recent pharmacological, genetic, or behavioral therapeutic intervention advancements that may alleviate age-related cardiac decline.

Defining the molecular underpinnings controlling cardiomyocyte proliferation

Shortly after birth, mammalian cardiomyocytes (CM) exit the cell cycle and cease to proliferate. The inability of adult CM to replicate renders the heart particularly vulnerable to injury. Restoration of CM proliferation would be an attractive clinical target for regenerative therapies that can preserve contractile function and thus prevent the development of heart failure. Our review focuses on recent progress in understanding the tight regulation of signaling pathways and their downstream molecular mechanisms that underly the inability of CM to proliferate in vivo. In this review, we describe the temporal expression of cell cycle activators e.g., cyclin/Cdk complexes and their inhibitors including p16, p21, p27 and members of the retinoblastoma gene family during gestation and postnatal life. The differential impact of members of the E2f transcription factor family and microRNAs on the regulation of positive and negative cell cycle factors is discussed. This review also highlights seminal studies that identified the coordination of signaling mechanisms that can potently activate CM cell cycle re-entry including the Wnt/Ctnnb1, Hippo, Pi3K-Akt and Nrg1-Erbb2/4 pathways. We also present an up-to-date account of landmark studies analyzing the effect of various genes such as Argin, Dystrophin, Fstl1, Meis1, Pitx2 and Pkm2 that are responsible for either inhibition or activation of CM cell division. All these reports describe bona fide therapeutically targets that could guide future clinical studies toward cardiac repair.

A high-resolution route map reveals distinct stages of chondrocyte dedifferentiation for cartilage regeneration

Articular cartilage damage is a universal health problem. Despite recent progress, chondrocyte dedifferentiation has severely compromised the clinical outcomes of cell-based cartilage regeneration. Loss-of-function changes are frequently observed in chondrocyte expansion and other pathological conditions, but the characteristics and intermediate molecular mechanisms remain unclear. In this study, we demonstrate a time-lapse atlas of chondrocyte dedifferentiation to provide molecular details and informative biomarkers associated with clinical chondrocyte evaluation. We performed various assays, such as single-cell RNA sequencing (scRNA-seq), live-cell metabolic assays, and assays for transposase-accessible chromatin with high-throughput sequencing (ATAC-seq), to develop a biphasic dedifferentiation model consisting of early and late dedifferentiation stages. Early-stage chondrocytes exhibited a glycolytic phenotype with increased expression of genes involved in metabolism and antioxidation, whereas late-stage chondrocytes exhibited ultrastructural changes involving mitochondrial damage and stress-associated chromatin remodeling. Using the chemical inhibitor BTB06584, we revealed that early and late dedifferentiated chondrocytes possessed distinct recovery potentials from functional phenotype loss. Notably, this two-stage transition was also validated in human chondrocytes. An image-based approach was established for clinical use to efficiently predict chondrocyte plasticity using stage-specific biomarkers. Overall, this study lays a foundation to improve the quality of chondrocytes in clinical use and provides deep insights into chondrocyte dedifferentiation.

CVD and COVID-19: Emerging Roles of Cardiac Fibroblasts and Myofibroblasts

Cardiovascular disease (CVD) is the leading cause of death worldwide. Current data suggest that patients with cardiovascular diseases experience more serious complications with coronavirus disease-19 (COVID-19) than those without CVD. In addition, severe COVID-19 appears to cause acute cardiac injury, as well as long-term adverse remodeling of heart tissue. Cardiac fibroblasts and myofibroblasts, being crucial in response to injury, may play a pivotal role in both contributing to and healing COVID-19-induced cardiac injury. The role of cardiac myofibroblasts in cardiac fibrosis has been well-established in the literature for decades. However, with the emergence of the novel coronavirus SARS-CoV-2, new cardiac complications are arising. Bursts of inflammatory cytokines and upregulation of TGF-β1 and angiotensin (AngII) are common in severe COVID-19 patients. Cytokines, TGF-β1, and Ang II can induce cardiac fibroblast differentiation, potentially leading to fibrosis. This review details the key information concerning the role of cardiac myofibroblasts in CVD and COVID-19 complications. Additionally, new factors including controlling ACE2 expression and microRNA regulation are explored as promising treatments for both COVID-19 and CVD. Further understanding of this topic may provide insight into the long-term cardiac manifestations of the COVID-19 pandemic and ways to mitigate its negative effects.

Spironolactone Inhibits Cardiomyocyte Hypertrophy by Regulating the Ca2+/Calcineurin/p-NFATc3 Pathway

This study aimed to investigate the protective effect and molecular mechanism of spironolactone in isoproterenol-induced cardiomyocyte hypertrophy. In this study, primary cardiomyocytes were extracted from the heart of neonatal rats. After stable culture, they were processed with isoproterenol alone or isoproterenol (10 μM) combined with different doses (low dose of 10 μM and high dose of 50 μM), and the cellular activity was determined by MTT experiment. The volume of cells was measured with an inverted microscope and CIAS-1000 cell image analysis system. The mRNA expression levels of ANP and BNP in cells were explored by RT-qPCR. The levels of ANP and BNP proteins and NFATc3 phosphorylation in the nucleus were detected by western blot. The extracellular Ca2⁺ concentration and CaN activity were measured by colorimetry with the kit. Isoproterenol significantly enlarged the volume of cardiomyocytes (p < 0.001), upregulated mRNA and expression levels of ANP and BNP proteins (p < 0.001), increased extracellular Ca²⁺ concentration and CaN activity (p < 0.001), and upregulated NFATc3 phosphorylation in the nucleus (p < 0.001). The volume of cells treated with isoproterenol combined with different doses of spironolactone significantly decreased compared with those treated with isoproterenol alone (p < 0.001). mRNA and expression levels of ANP and BNP proteins downregulated significantly (p < 0.001). The extracellular Ca²⁺ (p < 0.01) concentration and CaN activity (p < 0.001) decreased significantly, and NFATc3 phosphorylation in the nucleus downregulated significantly (p < 0.001). There was no significant difference in cell volume (p=0.999), ANP and BNP mRNA (p=0.695), expression levels of proteins, CaN activity (0.154), and NFATc3 phosphorylation in the nucleus between the cells treated with isoproterenol combined with high-dose spironolactone and those in the control group. In conclusion, spironolactone can reverse isoproterenol-induced cardiomyocyte hypertrophy by inhibiting the Ca²⁺/CaN/NFATc3 pathway.

Heart neurons use clock genes to control myocyte proliferation

Neurons can regulate the development, pathogenesis, and regeneration of target organs. However, the role of neurons during heart development and regeneration remains unclear. We genetically inhibited sympathetic innervation in vivo, which resulted in heart enlargement with an increase in cardiomyocyte number. Transcriptomic and protein analysis showed down-regulation of the two clock gene homologs Period1/Period2 (Per1/Per2) accompanied by up-regulation of cell cycle genes. Per1/Per2 deletion increased heart size and cardiomyocyte proliferation, recapitulating sympathetic neuron–deficient hearts. Conversely, increasing sympathetic activity by norepinephrine treatment induced Per1/Per2 and suppressed cardiomyocyte proliferation. We further found that the two clock genes negatively regulate myocyte mitosis entry through the Wee1 kinase pathway. Our findings demonstrate a previously unknown link between cardiac neurons and clock genes in regulation of cardiomyocyte proliferation and heart size and provide mechanistic insights for developing neuromodulation strategies for cardiac regen5eration.

Sodium-Glucose Cotransporter 2 Inhibitors Work as a "Regulator" of Autophagic Activity in Overnutrition Diseases

Several large clinical trials have shown renal and cardioprotective effects of sodium–glucose cotransporter 2 (SGLT2) inhibitors in diabetes patients, and the protective mechanisms need to be elucidated. There have been accumulating studies which report that SGLT2 inhibitors ameliorate autophagy deficiency of multiple organs. In overnutrition diseases, SGLT2 inhibitors affect the autophagy via various signaling pathways, including mammalian target of rapamycin (mTOR), sirtuin 1 (SIRT1), and hypoxia-inducible factor (HIF) pathways. Recently, it turned out that not only stagnation but also overactivation of autophagy causes cellular damages, indicating that therapeutic interventions which simply enhance or stagnate autophagy activity might be a “double-edged sword” in some situations. A small number of studies suggest that SGLT2 inhibitors not only activate but also suppress the autophagy flux depending on the situation, indicating that SGLT2 inhibitors can “regulate” autophagic activity and help achieve the appropriate autophagy flux in each organ. Considering the complicated control and bilateral characteristics of autophagy, the potential of SGLT2 inhibitors as the regulator of autophagic activity would be beneficial in the treatment of autophagy deficiency.

Establishment and analysis of the lncRNA-miRNA-mRNA network based on competitive endogenous RNA identifies functional genes in heart failure

Heart failure (HF), a common disease in adults, accounts for significantly global morbidity and mortality. Due to population aging, therapeutic progression in acute cardiovascular events, the prevalence of HF is increasing, in spite of the efficacy of multiple therapies for HF patients with decreased ejection fraction. Despite great progress in the underlying molecular mechanisms, it remains incompletely clear of the function of competing endogenous RNA (ceRNA) network in HF pathogenesis. Herein, we established an HF-related ceRNA network on the basis of differentially expressed long noncoding RNAs (lncRNAs), microRNAs (miRNAs) as well as mRNAs from GSE136547 and GSE124401 datasets. In brief, the ceRNA network composed of 58 mRNA nodes, 5 miRNA nodes, 82 lncRNA nodes as well as 252 edges. In addition, three lncRNAs (KCNQ1OT1, XIST and AC010336) with higher node degrees than other lncRNAs were chosen as hub nodes. At the same time, we have established five subnetwork of miR-17-5p, miR-20b-5p, miR-107, miR-125a-5p and miR-140-5p centered ceRNA. Pathway analysis revealed the enrichment of ceRNA network in cell cycle pathways. Collectively, our research sheds new lights on the essential functions of ceRNA network in HF development, which also suggests possible application of these hub nodes as diagnostic biomarkers as well as therapeutic targets.

Circular RNA circ_0010729 Knockdown Attenuates Oxygen-Glucose Deprivation-Induced Human Cardiac Myocytes Injury by miR-338-3p/CALM2 Axis

ABSTRACT

Circular RNAs have pivotal roles in cardiovascular disease. The injury of cardiac myocytes is associated with occurrence of cardiovascular disease. Circular RNA hsa_circ_0010729 (circ_0010729) is associated with cardiac myocytes injury. However, the mechanism of circ_0010729 in cardiac myocytes injury remains largely unclear. In our study, cardiac myocytes were treated by oxygen-glucose deprivation (OGD). The abundances of circ_0010729, microRNA-338-3p (miR-338-3p), and calmodulin 2 (CALM2) were detected by quantitative reverse transcription polymerase chain reaction or Western blot. OGD-induced damage in AC16 cells was assessed by cell viability, apoptosis, and autophagy using Cell Counting Kit-8, flow cytometry, and Western blot analyses. The target relationship of miR-338-3p and circ_0010729 or CALM2 was explored by starBase and dual-luciferase reporter analysis. Our results showed that the circ_0010729 level was enhanced in OGD-treated AC16 cells and murine primary cardiac myocytes. circ_0010729 silence weakened OGD-induced viability inhibition and promotion of apoptosis and autophagy in AC16 cells and murine primary cardiac myocytes. miR-338-3p was sponged by circ_0010729 and miR-338-3p knockdown alleviated the effect of circ_0010729 silence on OGD-induced damage. miR-338-3p directly targeted CALM2 to inhibit OGD-induced damage in AC16 cells. circ_0010729 could regulate CALM2 expression by sponging miR-338-3p. Collectively, circ_0010729 interference mitigated OGD-induced damage in cardiac myocytes through increasing cell viability and inhibiting apoptosis and autophagy by regulating miR-338-3p/CALM2 axis. This study indicated circ_0010729 might act as a target for treatment of cardiovascular disease.

Melatonin mitigates the adverse effect of hypoxia during myocardial differentiation in mouse embryonic stem cells

Background

Hypoxia causes oxidative stress and affects cardiovascular function and the programming of cardiovascular disease. Melatonin promotes antioxidant enzymes such as superoxide dismutase, glutathione reductase, glutathione peroxidase, and catalase.

Objectives

This study aims to investigate the correlation between melatonin and hypoxia induction in cardiomyocytes differentiation.

Methods

Mouse embryonic stem cells (mESCs) were induced to myocardial differentiation. To demonstrate the influence of melatonin under hypoxia, mESC was pretreated with melatonin and then cultured in hypoxic condition. The cardiac beating ratio of the mESC-derived cardiomyocytes, mRNA and protein expression levels were investigated.

Results

Under hypoxic condition, the mRNA expression of cardiac-lineage markers (Brachyury, Tbx20, and cTn1) and melatonin receptor (Mtnr1a) was reduced. The mRNA expression of cTn1 and the beating ratio of mESCs increased when melatonin was treated simultaneously with hypoxia, compared to when only exposed to hypoxia. Hypoxia-inducible factor (HIF)-1α protein decreased with melatonin treatment under hypoxia, and Mtnr1a mRNA expression increased. When the cells were exposed to hypoxia with melatonin treatment, the protein expressions of phospho-extracellular signal-related kinase (p-ERK) and Bcl-2-associated X proteins (Bax) decreased, however, the levels of phospho-protein kinase B (p-Akt), phosphatidylinositol 3-kinase (PI3K), B-cell lymphoma 2 (Bcl-2) proteins, and antioxidant enzymes including Cu/Zn-SOD, Mn-SOD, and catalase were increased. Competitive melatonin receptor antagonist luzindole blocked the melatonin-induced effects.

Conclusions

This study demonstrates that hypoxia inhibits cardiomyocytes differentiation and melatonin partially mitigates the adverse effect of hypoxia in myocardial differentiation by regulating apoptosis and oxidative stress through the p-AKT and PI3K pathway.

A surgical mouse model of neonatal pressure overload by transverse aortic constriction

Cardiac disease is the main cause of death worldwide. Insufficient regeneration of the adult mammalian heart is a major driver of cardiac morbidity and mortality. Cardiac regeneration occurs in early postnatal mice, thus understanding mechanisms of mammalian cardiac regeneration could facilitate the development of novel therapeutic strategies. Here, we provide a detailed description of a neonatal mouse model of pressure overload by transverse aortic constriction (nTAC) that can be applied at postnatal days 1 and 7. We have previously used this model to demonstrate that mice are able to fully adapt to pressure overload following nTAC on postnatal day 1. In contrast, when nTAC is applied in the non-regenerative phase (at postnatal day 7), it is associated with a maladaptive response similar to that seen when transverse aortic constriction (TAC) is applied to adult mice. Once a user is experienced in nTAC surgery, the procedure can be completed in less than 10 min per mouse. We anticipate that this model will facilitate the discovery of therapeutic targets to treat patients or prevent pressure overload-induced cardiac failure in the future.

Cancer cells employ an evolutionarily conserved polyploidization program to resist therapy

Unusually large cancer cells with abnormal nuclei have been documented in the cancer literature since 1858. For more than 100 years, they have been generally disregarded as irreversibly senescent or dying cells, too morphologically misshapen and chromatin too disorganized to be functional. Cell enlargement, accompanied by whole genome doubling or more, is observed across organisms, often associated with mitigation strategies against environmental change, severe stress, or the lack of nutrients. Our comparison of the mechanisms for polyploidization in other organisms and non-transformed tissues suggest that cancer cells draw from a conserved program for their survival, utilizing whole genome doubling and pausing proliferation to survive stress. These polyaneuploid cancer cells (PACCs) are the source of therapeutic resistance, responsible for cancer recurrence and, ultimately, cancer lethality.

Comparative Effect of MSC Secretome to MSC Co-culture on Cardiomyocyte Gene Expression Under Hypoxic Conditions in vitro

Introduction

Despite major leaps in regenerative medicine, the regeneration of cardiomyocytes after ischemic conditions remains to elucidate. It is crucial to understand hypoxia induced cellular mechanisms to provide advanced treatment options, including the use of stem cell paracrine factors for myocardial regeneration.

Materials and Methods

In this study, the regenerative potential of hypoxic human cardiomyocytes (group Hyp-CMC) in vitro was evaluated when co-cultured with human bone-marrow derived MSC (group Hyp-CMC-MSC) or stimulated with the secretome of MSC (group Hyp-CMC-S_MSC). The secretome of normoxic MSC and CMC, and the hypoxic CMC was analyzed with a cytokine panel. Gene expression changes of HIF-1α, proliferation marker Ki-67 and cytokinesis marker RhoA over different reoxygenation time periods of 4, 8, 24, 48, and 72 h were analyzed in comparison to normoxic CMC and MSC. Further, the proinflammatory cytokine IL-18 protein expression change, metabolic activity and proliferation was assessed in all experimental setups.

Results and Conclusion

HIF-1α was persistently overexpressed in Hyp-CMC-S_MSC as compared to Hyp-CMC (except at 72 h). Hyp-CMC-MSC showed a weaker HIF-1α expression than Hyp-CMC-S_MSC in most tested time points, except after 8 h. The Ki-67 expression showed the strongest upregulation in Hyp-CMC after 24 and 48 h incubation, then returned to baseline level, while a temporary increase in Ki-67 expression in Hyp-CMC-MSC at 4 and 8 h and at 48 h in Hyp-CMC-S_MSC could be observed. RhoA was increased in normoxic MSCs and in Hyp-CMC-S_MSC over time, but not in Hyp-CMC-MSC. A temporary increase in IL-18 protein expression was detected in Hyp-CMC-SMSC and Hyp-CMC. Our study demonstrates timely dynamic changes in expression of different ischemia and regeneration-related genes of CMCs, depending from the culture condition, with stronger expression of HIF-1α, RhoA and IL-18 if the hypoxic CMC were subjected to the secretome of MSCs.

A specialized population of Periostin-expressing cardiac fibroblasts contributes to postnatal cardiomyocyte maturation and innervation

During the postnatal period in mammals, the cardiac muscle transitions from hyperplasic to hypertrophic growth, the extracellular matrix (ECM) undergoes remodeling, and the heart loses regenerative capacity. While ECM maturation and crosstalk between cardiac fibroblasts (CFs) and cardiomyocytes (CMs) have been implicated in neonatal heart development, not much is known about specialized fibroblast heterogeneity and function in the early postnatal period. In order to better understand CF functions in heart maturation and postnatal cardiomyocyte cell-cycle arrest, we have performed gene expression profiling and ablation of postnatal CF populations. Fibroblast lineages expressing Tcf21 or Periostin were traced in transgenic GFP reporter mice, and their biological functions and transitions during the postnatal period were examined in sorted cells using RNA sequencing. Highly proliferative Periostin (Postn)+ lineage CFs were found from postnatal day 1 (P1) to P11 but were not detected at P30, due to a repression of Postn gene expression. This population was less abundant and transcriptionally different from Tcf21+ resident CFs. The specialized Postn+ population preferentially expresses genes related to cell proliferation and neuronal development, while Tcf21+ CFs differentially express genes related to ECM maturation at P7 and immune crosstalk at P30. Ablation of the Postn+ CFs from P0 to P6 led to altered cardiac sympathetic nerve patterning and a reduction in binucleation and hypertrophic growth with increased fetal troponin (TroponinI1) expression in CM. Thus, postnatal CFs are heterogeneous and include a transient proliferative Postn+ population required for cardiac nerve development and cardiomyocyte maturation soon after birth.

Cardiomyocyte cell cycling, maturation, and growth by multinucleation in postnatal swine

BACKGROUND

Rodent cardiomyocytes (CM) undergo mitotic arrest and decline of mononucleated-diploid population post-birth, which are implicated in neonatal loss of heart regenerative potential. However, the dynamics of postnatal CM maturation are largely unknown in swine, despite a similar neonatal cardiac regenerative capacity as rodents. Here, we provide a comprehensive analysis of postnatal cardiac maturation in swine, including CM cell cycling, multinucleation and hypertrophic growth, as well as non-CM cardiac factors such as extracellular matrix (ECM), immune cells, capillaries, and neurons. Our study reveals discordance in postnatal pig heart maturational events compared to rodents.

METHODS AND RESULTS

Left-ventricular myocardium from White Yorkshire-Landrace pigs at postnatal day (P)0 to 6 months (6mo) was analyzed. Mature cardiac sarcomeric characteristics, such as fetal TNNI1 repression and Cx43 co-localization to cell junctions, were not evident until P30 in pigs. In CMs, appreciable binucleation is observed by P7, with extensive multinucleation (4-16 nuclei per CM) beyond P15. Individual CM nuclei remain predominantly diploid at all ages. CM mononucleation at ~50% incidence is observed at P7-P15, and CM mitotic activity is measurable up to 2mo. CM cross-sectional area does not increase until 2mo-6mo in pigs, though longitudinal CM growth proportional to multinucleation occurs after P15. RNAseq analysis of neonatal pig left ventricles showed increased expression of ECM maturation, immune signaling, neuronal remodeling, and reactive oxygen species response genes, highlighting significance of the non-CM milieu in postnatal mammalian heart maturation.

CONCLUSIONS

CM maturational events such as decline of mononucleation and cell cycle arrest occur over a 2-month postnatal period in pigs, despite reported loss of heart regenerative potential by P3. Moreover, CMs grow primarily by multinucleation and longitudinal hypertrophy in older pig CMs, distinct from mice and humans. These differences are important to consider for preclinical testing of cardiovascular therapies using swine, and may offer opportunities to study aspects of heart regeneration unavailable in other models.

Rapid Development of Targeting circRNAs in Cardiovascular Diseases

Circular RNAs (circRNAs) are circularized, single-stranded RNAs that are covalently linked. With their abundance in tissues and developmental stage-specific expression, circRNAs participate in a variety of physiological and pathological processes. In this review, we discuss the development of circRNAs used as biomarkers and therapeutic targets for cardiovascular diseases (CVDs), focusing on recent discoveries and applications of exosomal circRNAs that highlight opportunities and challenges. Some studies have identified a spectrum of circRNAs that are differentially expressed in CVDs, while other studies further manipulated specific circRNA expression and showed an ameliorated pathogenic state such as ischemic injury, hypertrophy, and cardiac fibrosis. Studies and applications of circRNAs are being rapidly developed. We expect to see clinical use of circRNAs as biomarkers and targets for disease treatment in the near future.

Cardiac ageing: extrinsic and intrinsic factors in cellular renewal and senescence

Cardiac ageing manifests as a decline in function leading to heart failure. At the cellular level, ageing entails decreased replicative capacity and dysregulation of cellular processes in myocardial and nonmyocyte cells. Various extrinsic parameters, such as lifestyle and environment, integrate important signalling pathways, such as those involving inflammation and oxidative stress, with intrinsic molecular mechanisms underlying resistance versus progression to cellular senescence. Mitigation of cardiac functional decline in an ageing organism requires the activation of enhanced maintenance and reparative capacity, thereby overcoming inherent endogenous limitations to retaining a youthful phenotype. Deciphering the molecular mechanisms underlying dysregulation of cellular function and renewal reveals potential interventional targets to attenuate degenerative processes at the cellular and systemic levels to improve quality of life for our ageing population. In this Review, we discuss the roles of extrinsic and intrinsic factors in cardiac ageing. Animal models of cardiac ageing are summarized, followed by an overview of the current and possible future treatments to mitigate the deleterious effects of cardiac ageing.

Adult Cardiomyocyte Cell Cycle Detour: Off-ramp to Quiescent Destinations

Ability to promote completion of mitotic cycling of adult mammalian cardiomyocytes remains an intractable and vexing challenge, despite being one of the most sought after 'holy grails' of cardiovascular research. While some of the struggle is attributable to adult cardiomyocytes themselves that are notoriously post-mitotic, another contributory factor rests with difficulty in definitive tracking of adult cardiomyocyte cell cycle and lack of rigorous measures to track proliferation in situ. This review summarizes past, present, and future directions to promote adult mammalian cardiomyocyte cell cycle progression, proliferation, and renewal. Establishing relationship(s) between cardiomyocyte cell cycle progression and cellular biological properties is sorely needed to understand the mechanistic basis for cardiomyocyte cell cycle withdrawal to enhance cardiomyocyte cell cycle progression and mitosis.

Cardiomyocyte nuclearity and ploidy: when is double trouble?

Considerable effort has gone into investigating mechanisms that underlie the developmental transition in which mammalian cardiomyocytes (CMs) switch from being able to proliferate during development, to essentially having lost that ability at maturity. This problem is interesting not only for scientific curiosity, but also for its clinical relevance because controlling the ability of mature CMs to replicate would provide a much-needed approach for restoring cardiac function in damaged hearts. In this review, we focus on the propensity of mature mammalian CMs to be multinucleated and polyploid, and the extent to which this may be necessary for normal physiology yet possibly disadvantageous in some circumstances. In this context, we explore whether the concept of the myonuclear domain (MND) in multinucleated skeletal muscle fibers might apply to cardiomyocytes, and whether cardio-MND size might be related to the transition of CMs to become multinuclear. Nuclei in CMs are almost certainly integrators of not only biochemical, but also-because of their central location within the myofibrils-mechanical information, and this multimodal, integrative function in adult CMs-involving molecules that have been extensively studied along with newly identified possibilities-could influence both gene expression as well as replication of the genome and the nuclei themselves.

The Post-amyloid Era in Alzheimer's Disease: Trust Your Gut Feeling

The amyloid hypothesis, the assumption that beta-amyloid toxicity is the primary cause of neuronal and synaptic loss, has been the mainstream research concept in Alzheimer's disease for the past two decades. Currently, this model is quietly being replaced by a more holistic, “systemic disease” paradigm which, like the aging process, affects multiple body tissues and organs, including the gut microbiota. It is well-established that inflammation is a hallmark of cellular senescence; however, the infection-senescence link has been less explored. Microbiota-induced senescence is a gradually emerging concept promoted by the discovery of pathogens and their products in Alzheimer's disease brains associated with senescent neurons, glia, and endothelial cells. Infectious agents have previously been associated with Alzheimer's disease, but the cause vs. effect issue could not be resolved. A recent study may have settled this debate as it shows that gingipain, a Porphyromonas gingivalis toxin, can be detected not only in Alzheimer's disease but also in the brains of older individuals deceased prior to developing the illness. In this review, we take the position that gut and other microbes from the body periphery reach the brain by triggering intestinal and blood-brain barrier senescence and disruption. We also surmise that novel Alzheimer's disease findings, including neuronal somatic mosaicism, iron dyshomeostasis, aggressive glial phenotypes, and loss of aerobic glycolysis, can be explained by the infection-senescence model. In addition, we discuss potential cellular senescence targets and therapeutic strategies, including iron chelators, inflammasome inhibitors, senolytic antibiotics, mitophagy inducers, and epigenetic metabolic reprograming.

Coronary Vasculature in Cardiac Development and Regeneration

Functional coronary circulation is essential for a healthy heart in warm-blooded vertebrates, and coronary diseases can have a fatal consequence. Despite the growing interest, the knowledge about the coronary vessel development and the roles of new coronary vessel formation during heart regeneration is still limited. It is demonstrated that early revascularization is required for efficient heart regeneration. In this comprehensive review, we first describe the coronary vessel formation from an evolutionary perspective. We further discuss the cell origins of coronary endothelial cells and perivascular cells and summarize the critical signaling pathways regulating coronary vessel development. Lastly, we focus on the current knowledge about the molecular mechanisms regulating heart regeneration in zebrafish, a genetically tractable vertebrate model with a regenerative adult heart and well-developed coronary system.

Is adult cardiac regeneration absent in Xenopus laevis yet present in Xenopus tropicalis?

We recently used an endoscopy-based resection method to explore the consequences of cardiac injury in adult Xenopus laevis, obtaining the result that the adult Xenopus heart is unable to regenerate. At 11 months post-amputation, cellular and biological marks of scarring persisted. We thus concluded that, contrary to urodeles and teleosts, adult anurans share a cardiac injury outcome similar to adult mammals. However, in their work published in this journal on the 13 December 2017, Liao et al. showed that the adult Xenopus tropicalis heart is capable of efficient, almost scar free regeneration, a result at odds with our previous observation. These findings contrast with and challenge the outcome of adult heart repair following injury in Xenopus species. Here we discuss the question of the intrinsic cardiac regenerative properties of an adult heart in anuran amphibians.